There are a variety of ways to do this and all of them include simply being active. Ask and respond to a few questions when you don't have the ability or time to write and post hubs. I notice a fair number of hubbers reach a certain number of hubs and take a break from adding new ones but still have a decent score. They are actively reading and commenting on other hubs or actively engaging in the forums. Of course, if you do have the ability and time, you should be posting new hubs but there are a variety of ways to get your hub score at or above 85. Just remain active.